[docs] add note about pyodide support

[jameslamb]

This is SO COOL .... I learned tonight that Pyodide is building a version of the lightgbm Python package that runs in a web browser.

https://github.com/pyodide/pyodide/tree/main/packages/lightgbm

Try it yourself.... go to https://pyodide.org/en/stable/console.html (recommended from https://pyodide.org/en/stable/usage/index.html), and run the following:

import lightgbm as lgb
from sklearn.datasets import make_regression
from sklearn.metrics import r2_score

X, y = make_regression(n_samples=10_000, n_features=5, n_informative=5)
bst = lgb.train(
    train_set=lgb.Dataset(X, label=y),
    params={"objective": "regression", "verbose": -1}
)

print(r2_score(y, bst.predict(X)))
# 0.995701411473822

🤯 🤯 🤯 🤯

This proposes adding a note about that to the README.

[StrikerRUS]

LGTM! Interesting project indeed! I have never heard about it before.